Chemical analysis of small samples is important in the fields of environmental science, chemical process control, biotechnology, and medicine. In particular, the desire to make medical diagnoses at the point of care is driving the development of devices that can make accurate clinical chemical analyses of very small samples. The concept of a laboratory on a chip (LOC), 2(o incorporating small-scale versions of many chemical analysis devices (e.g., separators, reactors, Pa detectors) onto a single silicon chip (Jacobsen, S. C. et al. [1994], "Microchip capillary electrophoresis with an integrated postcolumn reactor," Anal. Chem. 66:3472-3476), is an active area of development.
The goal of chemical analysis is often to determine the concentration of constituents in a sample. The separation of the constituent of interest from interfering species is required before accurate concentration measurements can be made. In LOC devices, sample volumes are small (e.g. 100 nl). An effective method of constituent separation for such small samples is electrophoresis (Jacobsen et al., supra). Electrophoresis separates constituents axially along a flow channel due to differences in constituent mobilities. Species detection and concentration measurement is accomplished downstream of constituent separation in the same channel.
Small-scale separation techniques include split-flow thin (SPLITT) fractionation techniques (Fuh, C. B. and Giddings, J. C. [1995], "Isolation of human blood cells, platelets, and plasma proteins by centrifugal SPLITP fractionation," Biotechnol. Prog. 11:14-20; and Fuh, C. B. et al. [1993], "Rapid diffusion coefficient measurements using analytical SPLITT fractionation: applications to proteins," Analytical Biochemistry 208:80-87). These techniques involve substantially larger flow rates than the preferred devices used in the present invention.
A different, smaller-scale approach to constituent separation based on a T-sensor is described in Weigl et al., U.S. patent application Ser. No. 08/829,679 filed Mar. 31, 1997, now U.S. Pat. No. 5,972,710, PCT Application No. PCT/US97/05245 filed Mar. 31, 1997, and U.S. patent application Ser. No. 08/625,808 filed Mar. 29, 1996, now U.S. Pat. No. 5,716,852, all of which are incorporated herein by reference to the extent not inconsistent herewith.
A T-sensor operates by bringing a sample stream and an indicator stream into contact in a single channel. As constituents diffuse from the sample stream they react with a constituent in the indicator stream to produce a complex or change which can be detected, preferably by optical methods. A means for using this type of signal to determine the initial concentration in the sample of such constituents is needed rather than using a downstream detector as in Jacobsen et al., supra.
A device related to the T-sensor is the microscale diffusion-based separator described in Yager et al., U.S. patent application Ser. No. 08/663,916 filed Jun. 14, 1996, now U.S. Pat. No. 5,932,100, and PCT Publication No. WO 9700442 published Jan. 3, 1997, incorporated herein by reference to the extent not inconsistent herewith.
Publications containing subject matter by inventors hereof include Weigl, B. et al. (1996), "Diffusion-Based Optical Chemical Detection in Silicon Flow Structures," Analytical Methods & Instrumentation, Special Issue MTAS 96:174-184; and Galambos, P. et al. (1997), "A method for determination of pH using a T-sensor," 1997 International Conference on Solid State Sensors and Actuators (Transducers '97), Chicago, Ill., June 16-19, 1:535-538.
Means for determining initial concentrations of constituents in sample streams entering such devices is also needed.
All references discussed herein are hereby incorporated by reference in their entirety, to the extent not inconsistent herewith, particularly with respect to the teachings of art-known devices and procedures.